It is known that in an exhaust gas purification apparatus for an internal combustion engine which is provided with a selective catalytic reduction catalyst (SCR (Selective Catalytic Reduction) catalyst) arranged in an exhaust passage of the internal combustion engine, and a supply device for supplying an additive agent (e.g., urea aqueous solution), which is ammonia (NH3) or a precursor of ammonia, to the exhaust passage at the upstream side of the SCR catalyst, when the thermal deterioration of the SCR catalyst progresses, ammonia will be oxidized by the SCR catalyst, so that NOx will be produced (see, for example, Patent Literature 1).